The present invention relates to interleukin-18 (IL-18) binding protein, hereinafter IL-18BP, capable of binding IL-18. More particularly, this invention relates to a soluble IL-18BP obtainable from body fluids, to soluble IL-18BPs obtainable by expression of suitable DNA vectors in host cells, to virus-encoded homologues of IL-18BP obtainable by expression of suitable DNA vectors in host cells, to vectors expressing the various IL-18BPs, to vectors useful for expression of IL-18BP in humans and other mammals to antibodies against IL-18BPs, to therapeutic use of said IL-18BPs by modulating and/or blocking IL-18 activity, to therapeutic use of said expression vectors in modulating and/or blocking IL-18 activity and to use of the antibodies.
In 1989, an endotoxin-induced serum activity that induced interferon-xcex3 (IFN-xcex3) obtained from mouse spleen cells was described (27). This serum activity functioned not as a direct inducer of IFN-xcex3 but rather as a co-stimulant together with IL-2 or mitogens. An attempt to purify the activity from post-endotoxin mouse serum revealed an apparently homogeneous 50-55 kDa protein (26). Since other cytokines can act as co-stimulants for IFN-xcex3 production, the failure of neutralizing antibodies to IL-1, IL-4, IL-5, IL-6, or TNF to neutralize the serum activity suggested it was a distinct factor. In 1995, the same scientists demonstrated that the endotoxin-induced co-stimulant for IFN-xcex3 production was present in extracts of livers from mice preconditioned with P. acnes (31). In this model, the hepatic macrophage population (Kupffer cells) expand and in these mice, a low dose of bacterial lipopolysaccharide (LPS), which in non-preconditioned mice is not lethal, becomes lethal. The factor, named IFN-xcex3-inducing factor (IGIF) and later designated interleukin-18 (IL-18), was purified to homogeneity from 1,200 grams of P. acnes-treated mouse livers. Degenerate oligonucleotides derived from amino acid sequences of purified IL-18 were used to clone a murine IL-18 cDNA (31). IL-18 is an 18-19 kDa protein of 157 amino acids, which has no obvious similarities to any peptide in the databases. Messenger RNAs for IL-18 and interleukin-12 (IL-12) are readily detected in Kupffer cells and activated macrophages. Recombinant IL-18 induces IFN-gamma more potently than does IL-12, apparently through a separate pathway (31). Similar to the endotoxin-induced serum activity, IL-18 does not induce IFN-xcex3 by itself, but functions primarily as a co-stimulant with mitogens or IL-2. IL-18 enhances T cell proliferation, apparently through an IL-2-dependent pathway, and enhances Th1 cytokine production in vitro and exhibits synergism when combined with IL-12 in terms of enhanced IFN-xcex3 production (24).
Neutralizing antibodies to mouse IL-18 were shown to prevent the lethality of low-dose LPS in P. acnes pre-conditioned mice. Others had reported the importance of IFN-xcex3 as a mediator of LPS lethality in pre-conditioned mice. For example, neutralizing anti-IFN-xcex3 antibodies protected mice against Shwartzman-like shock (16), and galactosamine-treated mice deficient in the IFN-xcex3 receptor were resistant to LPS-induced death (7). Hence, it was not unexpected that neutralizing antibodies to murine IL-18 protected P. acnes-preconditioned mice against lethal LPS (31). Anti-murine IL-18 treatment also protected surviving mice against severe hepatic cytotoxicity.
After the murine form was cloned, the human cDNA sequence for IL-18 was reported in 1996 (38). Recombinant human IL-18 exhibits natural IL-18 activity (38). Human recombinant IL-18 is without direct IFN-xcex3-inducing activity on human T-cells, but acts as a co-stimulant for production of IFN-xcex3 and other T-helper cell-1 (Th1) cytokines (38). To date, IL-18 is thought of primarily as a co-stimulant for Th1 cytokine production (IFN-xcex3, IL-2 and granulocyte-macrophage colony stimulating factor) (20) and also as a co-stimulant for FAS ligand-mediated cytotoxicity of murine natural killer cell clones (37).
By cloning IL-18 from affected tissues and studying IL-18 gene expression, a close association of this cytokine with an autoimmune disease was found. The non-obese diabetic (NOD) mouse spontaneously develops autoimmune insulitis and diabetes, which can be accelerated and synchronized by a single injection of cyclophosphamide. IL-18 mRNA was demonstrated by reverse transcriptase PCR in NOD mouse pancreas during early stages of insulitis. Levels of IL-18 mRNA increased rapidly after cyclophosphamide treatment and preceded a rise in IFN-xcex3 mRNA, and subsequently diabetes. Interestingly, these kinetics mimic that of IL-12-p40 mRNA, resulting in a close correlation of individual mRNA levels. Cloning of the IL-18 cDNA from pancreas RNA followed by sequencing revealed identity with the IL-18 sequence cloned from Kupffer cells and in vivo pre-activated macrophages. Also NOD mouse macrophages responded to cyclophosphamide with IL-18 gene expression while macrophages from Balb/c mice treated in parallel did not. Therefore, IL-18 expression is abnormally regulated in autoimmune NOD mice and closely associated with diabetes development (32).
IL-18 plays a potential role in immunoregulation or in inflammation by augmenting the functional activity of Fas ligand on Th1 cells (10). IL-18 is also expressed in the adrenal cortex and therefore might be a secreted neuro-immunomodulator, playing an important role in orchestrating the immune system following a stressful experience (9).
In vivo, IL-18 is formed by cleavage of pro-IL-18, and its endogenous activity appears to account for IFN-xcex3 production in P. acnes and LPS-mediated lethality. Because of its activity, blocking the biological activity of IL-18 in human disease is a therapeutic strategy in many diseases. This can be accomplished using soluble receptors or blocking antibodies to the cell-bound IL-18 receptor.
Cytokine binding proteins (soluble cytokine receptors) correspond to the extracellular ligand binding domains of their respective cell surface cytokine receptors. They are derived either by alternative splicing of a pre-mRNA, common to the cell surface receptor, or by proteolytic cleavage of the cell surface receptor. Such soluble receptors have been described in the past, including among others, the soluble receptors of IL-6 and IFN-xcex3 (30), TNF (11, 12), IL-1 and IL-4 (21), IFN-xcex1/xcex2 (28, 29) and others. One cytokine-binding protein, named osteoprotegerin (OPG, also known as osteoclast inhibitory factorxe2x80x94OCIF), a member of the TNFR/Fas family, appears to be the first example of a soluble receptor that exists only as a secreted protein (1, 34, 39).
The present invention provides IL-18 binding proteins (IL-18BPs) and virally encoded IL-18BP homologues (hereinafter, viral IL-18BPs), and fused proteins, muteins, functional derivatives, active fragments and circularly permutated derivatives thereof, capable of binding to IL-18. The invention also provides a process for isolating IL-18BPs from human fluids, and a process to obtain them by recombinant means. The invention also provides expression vectors of IL-18BPs, suitable for expression of IL-18BP in humans and other mammals. Specific IL-18BPs, virally encoded IL-18BP homologues, fused proteins, muteins, functional derivatives, active fragments and circularly permutated derivatives thereof of the present invention are useful for modulating and/or blocking the biological activities of IL-18.
Replicable expression vehicles containing DNAs suitable for expression of the various IL-18BPs in host cells, host cells transformed herewith and proteins and polypeptides produced by expression of such hosts are also provided.
The invention further provides pharmaceutical compositions consisting of suitable vehicles and IL-18BPs, or viral IL-18BPs, or vectors for expressing same in humans and other mammals, for the treatment of diseases or conditions which require modulation or blocking of IL-18 activity.
The invention further provides antibodies to the IL-18BPs and the viral IL-18BPs, suitable for affinity purification and immunoassays of same.